stringByEvaluatingJavaScriptFromString doesn't fire JavaScript

when I press the up key in my web view, it logs it but it doesn't fire the JS alert as defined in stringByEvaluatingJavaScriptFromString, any ideas? Thanks

 - (void)applicationDidFinishLaunching:(NSNotification *)aNotification
    {
        [webView setMainFrameURL:@"http://google.com"];
        [webView setAutoresizingMask:NSViewWidthSizable | NSViewHeightSizable];

    }

     -(id)init {
        if( !(self = [super init]) ){
            return nil;
        }

        NSEvent * (^monitorHandler)(NSEvent *);
        monitorHandler = ^NSEvent * (NSEvent * theEvent){

            switch ([theEvent keyCode]) {
                case 123:    // Left arrow
                    NSLog(@"Left behind.");
                    break;
                case 124:    // Right arrow
                    NSLog(@"Right as always!");
                    break;
                case 125:    // Down arrow
                    NSLog(@"Downward is Heavenward");
                    break;
                case 126:    // Up arrow
                    [webView stringByEvaluatingJavaScriptFromString:@"alert('yo')"];
                    NSLog(@"Up, up, and away!");
                    break;
                default:
                    break;
            }
            // Return the event, a new event, or, to stop 
            // the event from being dispatched, nil
            return theEvent;
        };

        // Creates an object we do not own, but must keep track
        // of so that it can be "removed" when w开发者_如何转开发e're done
        eventMon = [NSEvent addLocalMonitorForEventsMatchingMask:NSKeyDownMask 
                                                         handler:monitorHandler];

        return self;
    }

A WebView will not display JavaScript alerts by default. In fact, you need to implement the code to display JavaScript alerts yourself, by setting an object as the delegate of the WebView and implementing the

‑webView:runJavaScriptAlertPanelWithMessage:initiatedByFrame:

delegate method.

However, in your case there's absolutely no reason to do this, since you can simply create a standard NSAlert. I don't understand why you're trying to make the WebView display the alert. Why not just display it directly?